Dollar Spot of Turfgrass
Causal Agent
Sclerotinia homeocarpa is the name that has been used for the fungus that causes dollar spot. However, recent studies have shown that the fungus most likely belongs in either the genus Lanzia or Moellerodiscus.
Hosts
Cultivated turfgrass species (bentgrass, bermudagrass, fescue, ryegrass, and zoysiagrass).
Symptoms
The overall symptom development for dollar spot varies with turfgrass species and
mowing practices. On closely mowed turfgrass, such as bentgrass golf greens, the characteristic
symptoms of dollar spot are small, circular, straw-colored, sunken spots that rarely
exceed 2-3 inches in diameter. If the disease becomes severe, individual spots may
coalesce forming larger, irregular patches of blighted turfgrass. Residential lawns
and other taller turfgrasses may exhibit irregularly shaped, bleached patches of blighted
grass ranging from 4-6 inches or more in diameter. Patches may coalesce to cover large
areas. Individual infected leaves develop a lesion(spot) that is first pale green
or yellow, then water-soaked, and finally a bleached straw color. Dollar spot lesions
are characteristically bounded by a tan to reddish-brown margin. These lesions usually
englarge to extend across the entire leaf. Dieback from leaf tips is also common.
Individual leaf blades may have a single lesion, have many small lesions, or be entirely
blighted. In the early morning when dew is present on grass blades and the pathogen
is active, a white, cottony, growth of fungal strands (mycelia) may be seen on diseased
turf. The mycelia disappear as the leaves dry.
Control
Cultural Management - Maintain moderate to high nitrogen fertility during periods
favorable for dollar spot development. For warm-season turfgrasses (bermuda and zoysia),
a total of five pounds actual nitrogen (N) per 1000 square feet should be applied
as five one-pound N per 1000 square feet split applications in May, June, July, August,
and September. Do not apply N after September 15, as this increases turfgrass susceptibility
to winter injury and spring dead spot disease development. For cool-season turfgrasses
(bent, blue, fescue, and rye), four pounds N per 1000 sq feet per year should be applied
as one pound N per 1000 sq feet applications in March, May, September, and November.
When water is required, apply a sufficient amount for deep penetration, and then water
as infrequently as possible without causing moisture stress between waterings. Avoid
frequent applications of small amounts of water. Do not water in the late afternoon
or evening, for this prolongs periods of leaf wetness at night. Promote good air circulation
over the turf by pruning or removing trees or shrubs and removing other barriers to
air movement. Mow the turfgrass regularly at recommended heights. Chemical Management
- If nitrogen fertility levels are properly managed, the use of fungicides for dollar
spot control in residential lawns is normally not necessary. However, many effective
fungicides are available for dollar spot management if needed. Chemical control is
most effective if different fungicides are alternated and applied in the early spring
and fall before disease development, or when the disease is first evident. Fungicides
should be used in conjunction with good turfgrass cultural management practices. Please
contact your local county extension office for current information.